Thanks for posting this question.
Our main concern with zero cycle retention is that you can be left without a backup to restore from as data aging is only counting against days and zero cycles.
That means if you have a primary copy set to 3 days and no backups run for 3 days data aging will still prune those jobs leaving you with nothing to recover from.
However, where it makes sense to use a zero cycle policy would be where your recovery requirements are only for X number of days. Then you can be certain that the data will be deleted and space recovered with no remaining cycle.
Let me know if this was helpful.